The resolution of the comparator is not defined by its offset: the comparator could still be able to discriminate (or resolve) a voltage difference of 1uV at its inputs while still having 10mV of systematic offset.
At any rate, the offset you see in the transient simulation is a dynamic offset due to many parameters, for instance due to kick back from the clock, charge injection if you use switches before the comparators for auto-zeroing, and so on... in the DC simulation you only see the systematic offset.